gCalMarkup allows Google Calendar™ events to be placed in categories.  There are several uses for categories:

To create and use categories:


They are also used to add attributes to categories of events, for example, the color.  The categories can be all events in a group , all events in a calendar, or all events with a specified category tag in the event content.  The category id defines which type of category is being created.  Any number of additional user parameters can also be added and used in gCalMarkup templates to indicate what category events are in.  For example: